Transistorized loading circuit



April 6, 1965 R. H. GRAHAM 3,177,373

TRANSISTORIZED LOADING CIRCUIT Filed Oct. 28, 1960 INVENTOR.

RICHARD H. GRAHAM A T TORNE Y United States I Patent the United States of America as represented by the United States Atomic Energy Commission Filed Oct. 28, 1960, Ser. No. 65,875 1 Claim. (Cl. 307-885) This invention relates generally to transistorizedswitching circuits and in particular relates to means for providing high voltage output from a characteristically low voltage circuit.

The advent of the transistor in the field of electronics has made possible numerous improvements over conventional vacuum tube circuitry with regards to such features as reliability, compactness, economy and portability. However, although advantageous in many respects, the fundamental nature of the transistor provides in general for only low voltage operation. Consequently, transistor circuitry has encountered much difiiculty in providing high voltage outputs comparable with that available from vacuum tube circuits, while still being able to retain adequate performance with regard to operational speed and economy.

In numerous applications of electronic switching circuits it is desirable to utilize relatively high voltage signals. For example, in the electronic computer art it is often required to have visual indication of the electrical state of the various computer switching circuits. In this regard, glow discharge lamps, such as neon lamps, are preferably used'to indicate, the output information from instruments such as counters, shift registers, and the like. Although glow discharge lamps are particularly suitable for these mentijonedutilizations, a relatively large voltage. is required tolfire and thereby light one. Thus, whereas neon lamps have been readily adaptable'for vacuum tube circuits, 'it is a more'difficult problem to use them with transistor circuitry.

For purposes of describing a preferred embodiment of the invention, infra, consider now the widelyused switch-. ing circuit known as arnultivibrator (hereinafter referred to as MV). The MV is ageneral class of switching circuits which include free running, bistable and monostable devices. As a' specific illustration, a conventional Eccles-Jordan bistable. MV is discussed herein, detailed reference to which is found in Junction Transistor Electronics, Richard B. Hurley, pp. 4244-27. 'As is readily observed, the bistable MV comprises two transistors, each in a grounded? emitter orientation, and coupled together in'a manner to keep one transistor in'a state of non conduction when the other has been triggered into a state of high conduction. Therefore, the two possible states of a MV transistor comprise, in general, conduc tion or non-conduction, these states being commonly referred to respectively as ON or OFF.

The conventional scheme for sampling or utilizing the information represented by the electrical state of an MV transistor is in general to couple an output load resistor between the MV collector and. ground. It is readily apparent, however, that the output voltage on the collector can be no larger than the MV supply voltage and therefore certainly for conventional 'MV circuits not large enough to fire a neon glow lamp. It should, of course, be noted that special high voltage transistors are available which can be incorporated into MV design. These high voltage transistors, which are incidentally expensive, if of good quality unfortunately present another problem of limited frequency response and ultimately of the MV speed of operation. More specifically, at low voltages a MV can be designed to operate in excess of megacycles, but the use of a high voltagegermanium transistor limits the MV operation to at best 100 kilocycles. It is MV transistor is not a feasible means of providing high voltage output signals.

A conventional means of obtaining a high voltage output from an MV is to couple an amplifier stage to the collector of the MV transistor. This approach becomes complex, however, because a single amplifier stage has a tendency to load down the MV and disrupt or degrade its operation. Thus to achieve high voltage output with low degradation in this manner requires a buffer stage interposed between thejMV collector output and the amplification stage. Asis readily evident, this approach requires two supplemental transistors in addition to each MV transistor thus creating a serious economic problem where a great plurality of MV circuits are employed,

as is often the case in a computer. Furthermore, the use of such cascaded stages also tends to limit the frequency capabilities of the over all circuit.

Now, as a solution to the instant problem the present invention afio-rds a simple and economical means for problem of a high voltage output from a fundamentally different point of view than do the conventional means. It may be noted from the foregoing remarks that conventional loading circuitry generally attempts to utilize the available voltage on the collector of the grounded emitter MV transistor. Thus at the outset conventional v circuitry must be prepared to provide high impedance loading to prevent degrading the MV operation. Even then minor fluctuations in the loading circuit may be able to disrupt the MV operation. -It is a basic intent of the present invention to load the MV circuit as painlessly as possible, that is, to extract the MV information while preventing the MV from becoming aware that it is being loaded. To achieve this result, the invention performs the loading operation at the emitter of a grounded emitter transistor. In essence, a transistor switch of vvirtually zero impedance is inserted into the MV emitter 'leg with this switch performing the high voltage switching operation. In this manner the present invention performs the heretofore difficult operation of providing high voltage output while preserving high frequency characteristics.

It is accordingly a primary object of the, present invention to provide a transistorized loading circuit "for providing high voltage output from a characteristically low voltage switching circuit.

It is another object of the invention to provide a loading circuit which offers virtually no degrading effects to the circuit being loaded.

It is still another object of the invention to provide a loading circuit capable of operating at as fast a speed as the circuit being loaded.

It is a further object of the invention to provide a high voltage loading circuit Which is particularly adaptable for utilization with transistorized multivibrator circuitry.

These and other objects and advantages of the present invention willbecorne more apparent upon consideration of the following description taken in conjunction with the accompanying drawing in which the sole figure is a schematic diagram of a preferred embodiment of the invention as incorporated into a bistable multivibrator circuit.

Referring now to the drawing, there is shown a con- Patented Apr. 6, 1965 manner as the transistor 12. g V is OFF, output terminal 27 exhibits substantially the l ventional Eccles-Jordan bistable MV circuit 11. Two identical and symmetrically disposed transistors 12 and 12 are the principal components of circuit 11 and their 7 electrical state determines. the, information state of the MV. More specifically, the MV circuit 11' has two stable information states, one of which is" represented by transistor 12 being ON and transistor 12' being OFF,

and the other state beingwhen transistor 12 is OFF and transistor 12 i ON; The remaining components of circuit 11 comprise a pair of identical cross coupling resistors 13 and 13' with resistor 13 coupled from the base of transistor '12 to the collector of transistor 12' and resistor 13' similarly connected between the base of transistor 12:

and the collector of transistor12. Apair of identical capacitors 14 and 14' are coupled respectively in parallel with resistors 13 and 13. Circuit 11 is powered byv a collector Isupply voltage applied to" terminal 16 and a base supply voltage applied to terminal 17. A pair of identical collec'torresistors 18 and 18' are connected respectively between the supply terminal 16 and the collectors of transistors 12 and 12 and a pair-of identical base resistors 19, and 19' are respectively coupled 'between supply terminal 17 and the bases of transistors 12 and 12'. It should be noted that circuit llas conventionally employed would have both the emitters 21 and 21 of transis tors Hand 12" connected directly to ground. The 'con- 1 ventional manner of infoumation utilization would then be to' directly employ thepotentials at the vcollector of transistor '12 or 12.

Now the present invention,'rather than having emitters 21 and 21' tied to ground, has these emitters coupled respectively to loading circuits 22 and 22?. Inasmuch as circuit 11 is completely symmetrical, the description here: inafter refers in general to only one side thereof, namely, transistor 12 and its associated loading circuit 22. The

principal component of circuit 22 is a grounded base transistor 24 which hasitsemitter 26 coupled to emitter 21. It is of particular importance to note that the transis tor 24 must be. of opposite polarity to the 'MV transistor 7 12'. That is, since transistor 12 ifof type NPN, transistor 2d musts'be PNP. I This latter specification is necessary to provide for a continuous current flow from emitter 21 into emitter 26, the need for which willbecome evident upon discussing the operation of the invention,

' infra.

With regard to the remaining components of circuit.

22 it is seen that transistor 24 has an output terminal 27 coupled directly to the collector 28 thereof; A negative battery supply 29 is then coupled from ground to collec- I ter 28 seriallythrouigh a load resistor 31. 7 As regards-the operation of the invention it Will becom apparent that instead of utilizing the collector potential to indicate theinformation state of the MV circuit 11, the

inventionutilizes the current conducted through the.

grounded emitter. transistor 12' to trigger an isolated external loading circuit 22 which is capable of handling It is note d'that the transistor relatively high voltages. 24 functions substantially as a switch in much the same Thus when transistor 24 negative potential of supply 29. When transistor 24 is ON, terminal 27 is brought to essentially ground potential. v

The advantages of the present invention are now explained by noting that emitter 21 of transistor 12 couples directly to the emitter 26 of grounded base transistor 24:1

In a state of high conduction, the input impedance to the emitter of a grounded base transistor isvirtually negligible. 'Thus emitteri21, which is conventionally coupled to ground, now couples into a transistor which offers essentially zero impedance thereto. Therefore when tranfunction is made possible by having coupledtogether the emitters of two oppositely'polarized transistors thereby allowing currentflow from one emitter into the other.

Thus, although emitter, 21 i grounded with regardto circuit 11, the emitter'current is performing the important funotion'of switching transistor24l into conduction. It

7 may. also he noted that when transistor 12 is OFF substantially no current flows therethrough and therefore transistor 24 is'als'o brought into-the OFF state. When transistor 12 is'OFF, it, of course, doesnot matter whether emitter 21 is grounded or not. It now becomes readily apparent that transistor 241s turnedONand OFF in sister 12 is ON, emitter 21 is still for all practical purposes coupled directly to' ground. However, when transistor 12 is ON, it is also feeding a high currentinto transistor 24 thereby turning it ON also. This latter exact. correspondence with the electrical state of transistor 12. lt'is further apparent'that transistor 24 is being switched by transistor .12 while transistor 12 is virtually unaware that it is performing this switching function.

A remaining feature ofimportance to note how is that a grounded base oriented transistor is-capable of holding otfia much higher collector potential than is a grounded emitter tstage. Thus transistor 24 of an inexpensive type can readily display voltage swings in excess of volts without any deterioration in frequency re sponse. Furthermore, transistor 12 can also 'be a simple inexpensive component not requirin any unusual charac teristics, Thusjthe only practical variable-in determining the voltage swing available at terminal 27' is the size of supply 29.

Itshould be emphasized that animportant' design criter-la for the present invention is that the loading circuit transistor 24 becomplimentary in polarity to transistor 12 of the MV'circuit. It is interesting to note that this characte'ristic makes it impossible to embody the present in-" vent-ion into a'vacuum tube circuit. 7

'Asa practical example ofthe invention consider now the following values given to the various components designated inthedrawingz 7 w V I The illustratedcircuit employing the above-described component values along with conventional clamping means can operate at a speed of the order of one megacycle; The voltage swing exhibited on the collector'of transistor 24? is substantially 45 volts asjis governed by the collector supply voltage.

on the collector of transistor 12. I

'It is thus evident thatthe present invention provides an excellent means for amplifying the output voltage of a conventional transistorized Eccles-Jordan bistable MV circuit without disrupting the operation thereof. It should be further pointed out that thezpresent invention can be utilized in almost any situation .where the output of a grounded emitter transistor is to be amplified without disrupting or loading down the loaded circuit." Therefore, inasmuch as the foregoing description Was made with particular reference to a preferred embodiment of the invention, it is to be understood that same was by way of example .and illustration only and is not to be taken. by way 'of limitation, the spirit and scope of this invention being limited only by the terms-of the appended claim.

What is claimed is:

'In a multivibrator circuit, the combination of a grounded emitter oriented transistor, said transistor being one of two crosscou pled transistors connected to a first power supply of one polarity with respect to ground for operation as a multivibrator, a transistor voltage pulse I This output voltage is al- I most three times as large. as the 16 volt swing available amplifier connected for receiving a direct input pulse from References Cited by the Examiner the multivibrator with a minimum loading effect on the UNITED STATES PATENTS multivibrator and for providing an amplifier output pulse,

said voltage amplifier comprising a resistor, a second powiifif i z 25:3 5 er supply of an opposite polarity with respect to ground, 5 2:963:648 12/60 Baskin et a1 307885 and a loading transistor having an emitter, base and a collector; said base being directly connected to ground; said emitter being directly series connected to the emitter of said grounded emitter oriented transistor for receiving the OTHER REFERENCES input from the multivibrator and for providing a low im- 10 pedance path to ground, said loading transistor having an opposite polarity to that of said grounded emitter oriented transistor, said resistor being connected between said 001- I IBM Tachmcal Dlsclosure Buuetm lector and said second power supply for reverse biasing February 1960- the collector-base junction and for deriving said amplifier output pulse, and an output terminal connected to said 15 ARTHUR GAUSS Primary Examiner collector of said loading transistor for providing such GEORGE N. WESTBY, JOHN W. HUCKERT, amplified output pulses. Examiners.

2,976,487 3/61 Cohen 30788.5

Junction Transistor Electronics, Hurley, John Wiley and Sons, 1958 (pages 424-427). 

